.m-mask{
  position:fixed;
  top:0;
  right:0;
  bottom:0;
  left:0;
  z-index:100;
  background-color: rgba(0,0,0,0.5);
  display:none;
  transition:0.3s;
  opacity:0;
  &[visible]{
    opacity:1;
  }
}